The large-scale, economic purification of proteins such as antibodies is an increasingly important problem for the biopharmaceutical industry. Therapeutic proteins are typically produced using prokaryotic or eukaryotic cell lines that are engineered to express the protein of interest from a recombinant plasmid containing the gene encoding the protein. Separation of the desired protein from the mixture of components fed to the cells and cellular by-products to an adequate purity, e.g., sufficient for use as a human therapeutic, poses a formidable challenge to biologics manufacturers for several reasons.
In the case of therapeutic antibodies, the current methods of purification involve the processing of large volumes of antibody-containing culture medium or cell lysates, from which the antibody is ultimately separated by chromatography. The rate limiting step in this method is the processing time associated with the large volume of antibody-containing starting material. One solution to this problem is to reduce the volume of the starting material by precipitating the antibody and resuspending in a smaller volume prior to performing the chromatography step(s). In addition, this precipitation step also partially purifies the protein of interest from other contaminants in the cell culture harvest. However, prior traditional protein precipitation methods have limitations for large scale production of therapeutics. For example, the common protein precipitant, ammonium sulphate, is corrosive and prone to releasing gaseous ammonia. Recent efforts at large scale antibody precipitation involved use of polyethylene glycol (PEG) as a precipitant (see US 2008/0214795, incorporated herein by reference in its entirety). However, this process can be challenging at large scale and the antibody precipitate so formed is difficult to resuspend in aqueous buffers.
Accordingly there is a need in the art for alternative antibody precipitation methods that can be used to expedite the large-scale processing of proteins, in particular antibodies.